The Douglas '029 and Douglas '036 applications (collectively, the "Douglas, et al., applications) disclose a massively parallel computer system including a number of processing nodes and control processors interconnected by a control network and a data router. Generally, the control processors control and synchronize processing by the processing nodes by means of commands transmitted over the control network. The processing nodes, as well as the control processors, can transfer data over the data router. The system is scalable, that is, the number of processing nodes and control processors can be varied depending on the processing requirements. The system is also partitionable through partitioning of the control network, which provides that commands from a control processor can be transmitted to selected ones of the processing nodes. Partitioning allows a system to process multiple applications concurrently, with each application being processed on a selected number of processing nodes. In addition, partitioning may be used to permit program developers to develop programs on partitions with small numbers of processors, without interfering with production processing on other, larger partitions.